1. Field of the Invention
The present invention relates to a hard coating excellent in wear resistance and in oxidation resistance and hard coating excellent in high-temperature anti-friction performance and in oxidation resistance and also a target for forming the hard coating, and particularly to a hard coating that is capable of improving the wear resistance, oxidation resistance and high-temperature anti-friction performance of cutting tools such as throwaway tool tip, drill bit and end mill, and to a target used as an evaporation source in the process of manufacturing the hard coating.
The hard coating of the present invention can be applied to such tools as end mill, drill bit, throwaway tool tip, gear cutting tool such as gear hob, punch-through tool, slitting cutter and plastic processing tools including extrusion die and forging die, that are made by using cemented carbide, cermet, high speed tool steel or the like. In the description that follows, cutting tools will be taken up as typical applications of the present invention.
2. Description of the Related Art
Coating of a tool with a hard coating such as TiN, TiCN or TiAlN has been applied to cutting tools that are used in high speed cutting or cutting of high hardness metals such as quench-hardened steel, for the purpose of improving the wear resistance of the cutting tools made of cemented carbide, cermet or high speed tool steel.
Further in recent years, it has been attempted to improve the properties by adding a third element as well as a tool metal of binary system such as (TiAl)N or (CrAl)N. For example, Japanese Unexamined Patent Publication (Kokai) No. 3-120354, Japanese Unexamined Patent Publication (Kokai) No. 10-18024 and Japanese Unexamined Patent Publication (Kokai) No. 10-237628 describe that excellent characteristics in cutting low-hardness materials such as S50C can be achieved by adding V to the coating material such as (CrAlV)N, (TiAlV)N, (CrAlV) (CN) or (TiAlV) (CN). However, these coating materials do not show sufficient cutting performance in machining of high-hardness materials such as quenched SKD material, and cannot satisfactorily allow it to increase the cutting speed. Thus a coating material having higher hardness and better wear resistance has been called for.
Japanese Unexamined Patent Publication (Kokai) No. 9-323204 describes a multi-layer coating film comprising layers made of Ti, Al and a nitride or carbonitride of a third component, the third component being at least one of Zr, Hf, Cr, W, Y, Si, Ce and Nb, while content of the third component is set in a range from 0.1 to 50% by the atomic ratio to Ti and Al. Japanese Unexamined Patent Publication (Kokai) No. 2004-130514 discloses a coating material having such a constitution that part of Cr atoms of (CrAlSi) (NBCO) are substituted with atoms of at least one of elements of groups 4, 5 and 6a and Y (substitution ratio is not higher than 30 atomic %). However, those proposed as the elements of groups 4, 5 and 6a and Y are only Ti, Zr and Hf, and addition of these elements is not considered to surely increase the wear resistance.
Japanese Unexamined Patent Publication (Kokai) No. 2004-100004 discloses a coating material represented by the formula: (Tia,Wb) (Cx,Ny)z where molar ratios of the components satisfy the relations 0.6≦a≦0.94, 0.06≦b≦0.4, a+b=1, 0.1≦x≦0.9, 0.1≦y≦0.9, x+y=1 and Z (total molar ratio of all non-metallic elements to the total metallic elements) satisfies the relation 0.8≦z≦1. As such materials, the following materials are exemplified: (Ti,W)C, (Ti,W,Nb)C, (Ti,W,Ta)C, (Ti,W,Ta,Nb)C, (Ti,W,Al)C, (Ti,W,Si)C, (Ti,W) (C,N), (Ti,W,Nb) (C,N), (Ti,W,Ta) (C,N), (Ti,W,Ta,Nb) (C,N), (Ti,W,Al) (C,N), (Ti,W,Si) (C,N), (Ti,W)N, (Ti,W,Nb)N, (Ti,W,Ta)N, (Ti,W,Ta,Nb)N, (Ti,W,Al)N, (Ti,W,Si)N. It is also described that the coating material represented by the formula: (Tia,Wb,Mc) (Cx,Ny)z where M represents at least one element selected from among Al, Si, Zr, Hf, V, Nb, Ta, Cr and Mo, while molar ratios of the components satisfy the relations 0.6≦a≦0.94, 0.06≦b≦0.4, 0≦c≦0.1, a+b+c=1, 0.1≦x≦0.9, 0.1≦y≦0.9, x+y=1 and z (total molar ratio of non-metallic elements C and N to the total metallic elements Ti, W and M) satisfies the relation 0.8≦z≦1. In particular, such a constitution as a base material made of a cemented carbide or a coating material includes at least one element selected from among Al, Si, Zr, Hf, V, Nb, Ta, Cr and Mo. However, the coating film that includes W is used only as an intermediate layer that improves the tenacity of the TiN or TiCN and the cemented carbide.
Japanese Unexamined Patent Publication (Kokai) No. 2003-211305 discloses a coating material represented by the formula: (Ti1-x,Wx) (C1-y,Ny) (where X is from 0.005 to 0.05 and Y is from 0.15 to 0.60 in an atomic ratio). This document describes the action of W by such a statement as “the W component gives high heat resistant plastic deformability to the (Ti, W)CN layer while maintaining the high strength and high toughness of the longitudinally grown crystal structure”.